What happens when sodium bicarbonate is heated?

What are the properties of NaHCO3 and Na2CO3 at high temperatures ( more than 500 K until 900 K)?
ortigosa@ari.ansaldo.it

Vocabulary
anhydrous*
Anhydrous sodium carbonate melts at 851°C (1124 K); however, it gradually decomposes in the temperature range you've specified, according to

Na2CO3(s) rightarrow CO2(g) + Na2O(s)

Sodium bicarbonate is even less stable with respect to heating. Solid NaHCO3 begins to lose carbon dioxide and water around 100°C, with complete conversion to sodium carbonate by 200°C:

2 NaHCO3(s) rightarrow CO2(g) + H2O(g) + Na2CO3(s)

In aqueous solution, carbon dioxide production begins at room temperature and decomposition of NaHCO3(aq) is essentially complete if the solution is brought to boiling.

The ease with which sodium bicarbonate loses carbon dioxide on heating is what makes it useful as "baking soda" and as a component in baking powders; channels opened by escaping carbon dioxide bubbles give baked goods a lighter and fluffier texture.

References

  1. Y. Otsubo, K. Yamaguchi, J. Chem. Soc. Japan, 82, 557-560 (1961).

Author: Fred Senese senese@antoine.frostburg.edu


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